It is known that photo enlargers fitted with dichroic color heads do not function automatically and are fitted with dial adjusted color correction filters in graduated densities of some 0 to 200 units of yellow, magenta and cyan, which must be set and adjusted manually in variable combinations and in accordance to the color densities contained in the negative and photographic paper dye layers. However, in new negatives and printing paper these densities are unknown and must be arrived at and correlated in the photographic paper through the progressive printing and evaluation of trial-and-error test prints which are exposed in a number of steps, using for each step a different combination of filter factor settings of determined value. After the test print is processed each of the stepped segments will show a contrasted color balance, or tint, and one of the exposed segments will indicate to the operator the most acceptable basic filter pack to use for the next group of tests, or for the initial test print of an enlargement.
To minimize the number of test prints required, the enlarger operator may employ one of several printing aid devices available; such as, the Kodak Ektacolor Filter Finder Kit or one of the electronic color analyzers such as the pmlA unit by Beseler or the new PCA2060 unit by Philips. However, these and other systems devices still require one or more test exposures to be made for the final correct determination of a filter pack to use for a given negative, particularly in the case of difficult to analyze problem negatives. Also, test prints are required when programming analyzers and to check the readouts. Analyzers must also be re-programmed by test printing each time a new paper pack is introduced because of the differences in dye layer characteristics from one emulsion number to another. In addition, a color print may show an undesirable color tint in the direction of any one of the six colors seen in the color wheel or in any combination of colors including the intermediate hues, making corrective color filter determination extremely difficult for the inexperienced printer.
The following publication is referred to by way of background material and from which the following excerpts are taken: Printing Color Negatives--Kodak No.E.66 Cat 155-1498-6-78-AXX major revision
"Making color balance corrections can be frustrating until you've gained some experience. A helpful technique that can save you much time is to record the exposure and filteration for each print right on the print" . . . "If you are making a series of test prints, it is also helpful to number them consecutively. This information is valuable for showing you exactly what effect the corrections you made had on the way the prints look." . . . page21 PA1 When a flat opaque card, having the one uniform tone of an 18% light reflectance grey, is accurately and evenly daylight illuminated in a manner which allows no particular color hue to be detected, is then properly photo-processed, it can be said that the resulting negative is to all intents and purposes a neutral grey. In the photographic printing trade such a negative is known as a standard `grey-card` negative and is used in test printing to determine the color printing characteristics of the photographic paper emulsion dye layers, which by a progressive and systematic modification of the filter pack color densities can be made to match the neutral grey value of the grey-card which was photographed; at which point the filter pack is effectively neutralized and coordinated with the photographic paper in use. So that, identically exposed negative type film can be more efficiently printed using the basic filteration which was determined to be correct for the grey-card negative.